The present invention relates to a data storage device, a data storage apparatus, and methods for writing and reading data.
With development in information storage technique, various storage devices are proposed. Especially, optical storage device is widely used because it has the merits of fast rate, small volume, long lifetime, and the like. The existing optical storage device generally has a disc form and information carried on the optical disc is converted into digits “0” and “1” corresponding to pits and lands on the optical disc, respectively. Pits having different lengths and lands between pits form spiral tracks extending from the inner side to the outer side of a disc, thereby recording data.
Pits and lands may be formed on an optical disc to record data in two ways, i.e., by laser ablation or laser irradiation, corresponding to write-only-read-many (WORM) disc and rewritable disc, respectively. In the way of laser ablation, a line-polarized collimated laser beam having a predetermined wavelength is modulated according to information to be recorded so as to obtain a series of laser pulses containing the information to be recorded. The laser pulses are focused by a optical system to form a well-focused light spot, which is used to ablate a recording layer containing dye so as to form pits, and lands are formed by portions of the optical disc that are not ablated. Thus, information is recorded into the optical disc. In the way of laser irradiation, phase change material is adopted for the recording layer of the optical disc such that the disc may be rewritable by changing phase state of the phase change material. In writing, intensity of the irradiated laser is set at its maximum to quickly heat the phase change material in a writing area to above the melting temperature. Then, the laser irradiation is stopped and the melted phase change material is cooled and forms an amorphous state. In erasing, a laser beam having a middling intensity is irradiated on the area of an amorphous state for relatively long time and the intensity is set lower when the temperature in the area rises beyond the melting point. Thus, the area is annealed to return to a crystal state.
However, the above technologies have shortcomings. As to the laser ablation method, the optical storage device can not be rewritten. As to the laser irradiation, the optical storage device may be rewritten only limited times. When the phase change material transforms between crystal and amorphous states limited times, the lattice geometry is gradually degraded to some extent, thereby rewritability of the device and reliability of information recording and reproducing degrade gradually.